1. Field of the Invention
The present invention relates to method of manufacturing a stator of a rotary electric machine such as an ac generator for a vehicle and, particularly, a method of twisting a plurality of conductor segments, which are welded to one another to form a stator coil.
2. Description of the Related Art
In order to meet the demand of a high-power vehicle ac generator, the following stator has been proposed. In the stator, I or U-shaped conductor segments are inserted into a plurality of slots of a stator core in one direction and welded to form a stator coil. Because the conductor segments can be regularly disposed in the stator core, the stator of this type provides a high conductor space factor and a high power capacity.
In order to provide such a stator coil from the above-described conductor segments, it is necessary to connect ends of the conductor segments to one another. WO92/06527 discloses a method of forming a stator coil by connecting a plurality of conductor segments disposed in a stator core.
In the above conventional technology, there are outer conductor segments inserted in the radially outer layer of the slots and inner conductor segments disposed in the radially inner layer of slots. Straight portions of the inner conductor segments and outer conductor segments are respectively twisted a half pole-pitch by twisting tools in the circumferential directions of the stator core opposite to each other. Thereafter, the ends of those of the conductor segments that are twisted are welded to adjacent ends of other conductor segments that are also twisted in the same manner to form a stator coil.
The twisting tools in the conventional method move only in the circumferential directions of the stator core. Although the segment""s ends can be properly located in the circumferential direction, they can not be located properly in the axial direction.
If the twisting tools are rotated the same angle, the ends of the outer conductor segments shift more than the ends of the inner conductor segments. In other words, if both the outer and inner conductor segments extending in the axial direction from the stator core have the same height, the outer conductor segments become lower than the inner conductor segments after they are twisted.
Accordingly, it is not possible to connect the outer and inner conductor segments without relocation of the conductor segments.
Therefore, an object of the invention is to provide an improved method of manufacturing a stator in which a plurality of conductor segments is disposed in a plurality of radially aligned layers of slots of a stator core. In the improved method, a plurality of outer and inner conductor segments extending from outer and inner layers of slots is twisted and located at desired positions to be readily connected to form a stator coil.
A main feature of the invention is a method for manufacturing a stator of a rotary electric machine that includes the following steps: forming a plurality of conductor segments each having at least a straight leg, inserting the plurality of conductor segments into slots of a stator core in a plurality of radially aligned layers so that the straight legs can extend from an end of the stator core, stratifying the straight legs in radially aligned layers to correspond to the layers in the slots, holding each of the straight legs at grip portions; circumferentially shifting each of the grip portions in a prescribed circumferential direction of the stator core; and axially shifting each of the grip portions separately from another in an axial direction of the stator core to locate those of the grip portions to be connected adjacent to each other.
According to a second feature of the invention, the straight legs are formed so that those of the grip portions of the legs disposed in radially more outside layer are higher.
The circumferential shift of the grip portions increases as the grip portions are disposed more radially outside. Therefore, the height of the grip portions disposed in the radially more outside layer is set higher so that the height of all the grip portions disposed in the respective layers can be made equal after they are twisted.
According to a third feature of the invention, each of the grip portions is shifted the same angle in the circumferential direction in the circumferentially shifting step, and each of the grip portions is shifted in the axial direction until all the heights become equal in the axially shifting step.
Therefore, the grip portions adjacent to each other can be easily connected.
According to a fourth feature of the invention, the grip portions are held so that distances between the grip portions and the end of the stator core can be equal to each other.
According to another feature of the invention, the grip portions are shifted the same angle in the circumferential directions, and the grip portions are separately shifted in the axial direction so that a length of one of the grip portions disposed in a radially more outside layer is shorter than another.
In the meantime, in an ordinary ac generator, cooling air is supplied outward from a radially inside portion of stator core 1. According to this feature of the invention, the axial position of the grip portions disposed in radially more outside layer is different from the axial position of those disposed in another layer.
According to another feature of the invention, the grip portions are held so that the length of one of the grip portions from the end of the stator core disposed in a radially more outside layer is longer.
Therefore, the height of the grip portions disposed in all the layers after being twisted are made equal to each other.
According to another feature of the invention, all the grip portions are shifted the same angle in circumferential directions, and the grip portions are separately shifted in the same axial direction so that the grip portions disposed in all the layers become equal in length.
According to another feature of the invention, the grip portions are held at circumferential sides thereof.
According to another feature of the invention, the grip portions are held while the grip ends thereof abut bottoms of cavities of holding members. Therefore, the grip portions are protected from damage.
According another feature of the invention, each of holding members have rectangular cavities for holding the grip portions to twist the extended legs.
Therefore, the holding members of the twisting means can be made simple.
According to another feature of the invention, a twisting apparatus includes a plurality of twisting tools moving in a circumferential direction of the stator core and in a axial direction thereof, circumferential driving units for moving the twisting tools in circumferential directions, and axial driving units for separately moving the twisting tools.
In this specification, the circumferential direction of the stator core is referred to as the core-circumference direction, and the axial direction of the stator core is referred to as the core-axis direction.